The national capital on Saturday recorded its coldest day of the season as the minimum temperature plummeted to 2.4 degrees Celsius, officials said.
The mercury even plunged to below two degrees in some areas with the Lodhi Road Observatory recording a low of 1.7 degrees Celsius.
Dense fog enveloped the city reducing visibility and affecting air and rail traffic and vehicular movement in the streets.
The Safdarjung Observatory, whose reading is considered the official marking for the city, recorded 2.4 degrees Celsius in the morning, five notches below the normal.
The same temperature was recorded on December 30, 2013. Before that the coldest day in December was December 11, 1996 when minimum temperature recorded at the observatory was 2.3 degrees Celsius, officials said.
The all-time record of low in Delhi is zero degree Celsius on December 27 in 1930, senior meteorologist at IMD, Kuldeep Srivastava said.
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Other observatories on Saturday recorded as follows: Palam 3.1 degrees Celsius, Aya Nagar 1.9 degrees Celsius, he said.
Due to very dense fog, zero visibility was reported in Palam Observatory area, which neighbours the city airport.
Due to heavy fog on Saturday morning, four flights were diverted from Delhi airport, said an airport official.
The official said that the flights were operating at the airport under CAT III B conditions, which means that the runway visual range (RVR) is between 50 metre and 175 metre.
According to railway officials, 24 trains were delayed due to poor visibility, ranging from 2-5 hours. Howrah New Delhi Poorva Express delayed by five hours.
The air quality turned severe again on Saturday, as falling temperatures, high humidity and low wind speed allowed accumulation of pollutants. The overall air quality index stood at 413 at 10 am.
With bone-chilling cold continuing to sweep Delhi-NCR, the weatherman said that the mercury is likely to fall further on Sunday too.
Cold wave and severe cold day and dense to very dense fog has been forecast over Delhi-NCR on Sunday and Monday, Srivastava said.
Mean maximum temperature (MMT) for December 2019 till 28th December stood at 19.18 degrees Celsius, he said.
By that yardstick, it is most likely to become second coldest December since 1901 (coldest was 17.3 degrees Celsius on December 1997).
The Safdurjung Observatory recorded a high of 13.3 degrees Celsius on Saturday evening, seven notches below the normal.
Even in the evening, the fog continued to envelope the city, as people huddled around bonfires lit up around railway stations, street sides and various other open spaces to ward off the chill.
Less people were seen at India Gate as many preferred to stay indoors to keep warm, despite being a weekend.
The relative humidity in the city recorded in the morning was 100 per cent and it reduced to 83 per cent in the evening.
"The mean maximum temperature for December was less than 20 degrees Celsius only in 1919, 1929, 1961 and 1997," an official of the India Meteorological Department said.
In December this year, the mean maximum temperature (MMT) till Thursday was 19.85 degrees Celsius. It is expected to dip to 19.15 degrees Celsius by December 31, he said.
Since December 14, most parts of the city have witnessed 15 consecutive "cold days" or a 15-day "cold spell". The last time such a long cold spell was witnessed was in December 1997.
After 1992, Delhi has had cold spells only in four years - 1997, 1998, 2003 and 2014.